This invention relates to heat exchangers and more particularly to heat exchangers of the side-entry type and to a method of making the same.
Side-entry type heat exchangers have a plurality of cross-fins with open-ended notches formed in their marginal edge portions. The notches in the cross-fins are aligned in rows, and heat exchanger tubing is inserted transversely into the aligned notches, threading the notches from row to row. The provision of open-ended notches along the marginal edges of the fin arrays enables the use of a one-piece heat exchanger tube.
Although the inner diameter of the notches in the fins corresponds to the outer diameter of the tube, the peripheral contact between the fins and the tube is reduced by at least the width of the open-end portion of the notch through which the heat exchanger tube is inserted into the fin array. Accordingly, to maximize contact between cross-fins and the heat exchanger tube, it is common practice in the manufacture of side-entry type heat exchangers to form the notches with a relatively narrow entry or throat portion leading into a generally circular relatively large diameter portion sized to the outer diameter of the heat exchanger tube. During the assembly of the tube the fin array, the tube is slightly flattened from its circular cross-section to facilitate its insertion transversely through the entry portion of the notch into the circular portion of the notch. The tube is then expanded by subjecting the tube to internal high pressure. Such expansion both interlocks the cross-fins and the tube against removal and enhances peripheral contact between the tube and the fin array.
One known arrangement for assembling a heat exchanger tube on such fin array includes preforming the tube to a helical shape and pressing the preformed tube into the notches of the fin array. Such method of assembly is not well suited for mass production because of the need to insert the fin assembly into the preformed tube, align each pass of the tube with an associated row of notches in the fin array and then press each tube section into its associated notches.
A further consideration is that assembling of a one-piece heat exchanger tube on such fin array requires forming of return bend portions to provide multiple passes of the heat exchanger tube along the surfaces of the fin unit. Although such bending causes "kinking" of the tube, usually any kinks in the return bend portions will be "blown out" when the tube is subjected to internal high pressure during expansion of the tube to engage the side walls of the body portions of the fin assembly. However, some of the portions of the heat exchanger tube which define the return bends may not be returned to their original circular cross-diameter shape, resulting flow restriction in one or several of the return bends, reducing the efficiency of the heat exchanger assembly.
Thus, it would be desirable to have a side-entry type heat exchanger of the type employing a one-piece heat exchanger tube which when assembled with a fin array, is substantially free of flow restriction in return bend portions.